An autoinjector is an automatic injection device designed to facilitate automated delivery of a dose of medicament to a patient through a hypodermic needle, the injection usually being administered by the patient themselves. An autoinjector works, for example, by delivering an injection automatically upon actuation by the patient pressing a button, moving a lever or part of a housing etc. This is in contrast to a conventional manual syringe where the patient himself needs to directly depress a plunger into a barrel containing medicament in order to effect the injection. The terms “autoinjector” and “injection device” are used interchangeably in the following description.
Examples of autoinjectors are described in WO2003/099358 (Seedlings Life Science Ventures LLC) and WO01/93926 (Mayo Foundation for Medical Education and Research). These are both generally flat devices which are of small size to encourage users to carry the device with them for ready access. GB2396298 (PA Consulting Services Ltd) is an example of a more conventionally-shaped elongate autoinjector, but of relatively complex internal construction.
All three of the above prior art devices have a custom designed medicament chamber therein rather than being built around a standard pre-filled syringe presentation. The custom medicament chamber, although allowing for a compact overall size for the device, means that the device as whole must be subjected to more rigorous regulatory control as compared with a device containing a standard pre-filled syringe presentation which will have already obtained regulatory approval.
In general, an autoinjector includes a needle which is located within the housing of the device. Upon activation of a force-generating source, a portion of the needle extends out of the housing and penetrates the outer layer of skin to deliver medicament. In some known autoinjectors, after activation, a needle cover or needle shield moves forward to conceal the needle after use. In GB2396298, the needle automatically retracts back into the housing by means of a biasing spring.
An improved autoinjector is described in our international patent application, published under number WO 2005/070481. Some of the reference numerals in the present application correspond with the equivalent components in the device described in WO 2005/070481. This device requires that the needle is moved axially so that it can appear beyond the end of the nozzle for the duration of the injection, after which the needle retracts automatically, so that it is never in sight of the user. The device also requires that the plunger is moved axially so that medicament is ejected. The overall complexity of the autoinjector is significantly reduced by both of these requirements being effected by one component, namely an inner housing and the device has the significant advantage that it can be built around a conventional or standard syringe presentation.
The injection device of WO 2005/070481 is designed to be used in conjunction with a standard drug presentation e.g. a pre-filled syringe comprising a needle, barrel pre-filled with medicament and a plunger. The plunger may include a separately-provided plunger rod. As mentioned above, there is a significant commercial advantage in being able to use a standard pre-filled syringe, which will have been subjected to numerous clinical trials, drug stability studies and regulatory approval. Any modification to the standard syringe may require further trials and approval, adding delay and expense.
In use, as described in WO 2005/070481, there are three stages of delivering an injection. Before delivering an injection (referring to FIG. 1 of the present application), the end cap 15 is pulled off, removing the needle cover 17 (if present) and rubber needle sheath 16 with it from the needle. In the first stage of delivering an injection, as shown in FIG. 2 of the present application, the tags 7B at the forward end of the inner housing 7 are in contact with the syringe barrel 90, which is pushed axially forward (taking the syringe holder 9 with it), so that the needle 10, which is fixed to the front end of the barrel, moves in the direction indicated by the arrow so that eventually it protrudes beyond the nozzle 11 at the front of the device. Forward travel of the barrel and syringe holder is limited when a surface 9A of the syringe holder reaches an endstop 11A inside the nozzle or front housing 11.
Referring now to FIG. 3, the second stage of the injection is the delivery of the medicament wherein the tags 7A at the rear of the inner housing 7 depress the plunger 8 into the barrel of the syringe in order to deliver medicament to the injection site.
In the third stage of the injection (not illustrated in the present application but shown in WO 2005/070481), once the medicament has been delivered and the inner housing 7 is no longer in contact with the barrel or plunger of the syringe, the secondary spring 12 automatically pushes the syringe holder (and hence the syringe contained therein) axially rearwardly so as to retract the syringe back into the housing so that the used needle is concealed from view.
In our application WO 2007/083115 (see FIG. 5) the syringe holder 9 is replaced by a syringe holder 100 (or “syringe support”) that comprises an elongate rear portion 102 a barrel seat 101 (equivalent to barrel seat 91 in FIGS. 1-3) at the rear end of the rear portion 102. The syringe holder also has an intermediate portion 105 of comparable diameter to the rear portion 102, and a front portion 106 of narrower diameter. The intermediate portion 105 is provided with a discontinuous annular flange 104.
WO 2007/083115 discloses a modified front housing 200 (analogous to nozzle 11 in FIGS. 1-3) which is illustrated in FIG. 4. The front housing 200 has a bore 201, of sufficient diameter to allow passage therethrough of the needle, a needle cover and front and intermediate portions of the syringe holder.
The interior surface of the bore 201 is provided with two (or more) equispaced longitudinal slots 202, each having a rear section 203 with a tapered surface providing a varying depth and a forward section 204 of substantially constant depth. The boundary between the forward and rear sections of each slot 202 is defined by a step 205.
The slots 202 provide axial and radial location for the syringe holder 100 as it is inserted therein.
The front housing 200, end cap 300 and syringe holder 100 are supplied in this ready-assembled condition, together with the ready-assembled rear part of the injection device, for final assembly with a pre-filled syringe.
FIG. 6 shows the fully assembled injection device including syringe holder 100. It can be seen that (unlike in the device of FIGS. 1-3) the flange 90 of the barrel does not contact the barrel seat 101 of the syringe holder 100, there being a gap G therebetween. This is a result of the relative axial positions of the syringe holder and syringe being determined at the front end, by gripping means 109 and a front shoulder 92 of the syringe 90.
The devices shown in WO 2005/070481 and WO 2007/083115 automatically retract the needle immediately after dose of the medicament has been delivered. This requires no intervention from the user. However, in some cases, automatic retraction may be undesirable as it could lead to the medicament siphoning back up the needle and out of the patient. In addition, excessively quick retraction of the needle after delivery may cause the medicament to escape from the puncture hole created by the needle in the tissue. This is a known problem when using adrenaline for example.